The present invention relates generally to ink jet printheads and, more particularly, to an improved method and apparatus for bonding a nozzle plate to the nozzle face of an ink jet printhead.
In ink jet printing, a printhead is usually provided having one or more ink-filled channels communicating with an ink supply chamber at one end and having an opening at the opposite end, referred to as a nozzle. These printheads form images on a recording medium such as paper by expelling droplets of ink from the nozzles onto the recording medium. The ink forms a meniscus at each nozzle prior to being expelled in the form of a droplet. After a droplet is expelled, additional ink surges to the nozzle to reform the meniscus. An important property of a high quality printhead array is good jet directionality. Good jet directionality ensures that ink droplets can be placed precisely where desired on the print document. Poor jet directional accuracy leads to the generation of deformed characters and visually objectionable banding in half tone pictorial images.
A major source of ink jet misdirection is associated with improper wetting of the nozzle surface of the printhead which contains the array of nozzles; e.g., the nozzle face. One factor which adversely affects jet directional accuracy is the interaction of ink accumulating on the nozzle face of the printhead array with the ejected droplets.
Various techniques have been used to reduce or eliminate the ink accumulation to improve directionality at the nozzle face. A preferred technique is to bond a thin polymeric film (referred to as a nozzle plate) to the printhead nozzle face and, using a mask, form holes through the film connecting to the channels of the printhead. This technique is disclosed, for example, in U.S. Pat. Nos. 5,434,607 and 5,493,320.
A preferred method for forming the holes in a nozzle plate is by laser ablation. For this technique, as shown in FIG. 1, a UV excimer laser 2 emits a beam of radiation which is directed through holes 4 of a mask 6 to a portion of a thin polymeric film 8, a portion of which will form a nozzle plate 10. The energy level and pulse repetition rate of the laser are controlled to form nozzle holes 12 in plate 10. Plate 10 is then aligned with nozzles 14 formed on the front face 16 of a printhead 18. Further details of a nozzle plate formed by laser ablation are disclosed in co-pending application U.S. Ser. No. 08/818,846 filed on Mar. 17, 1997 abandoned Apr. 30, 1998 and assigned to the same assignee as the present invention. This application, and the patents referenced supra, are hereby incorporated by reference.
For all the above-cited prior art references, the nozzle plate must be securely bonded to the nozzle face of the printhead and must be accurately aligned so that the holes formed in the nozzle plate are in precise alignment with the nozzle orifices; e.g., that holes 12 are aligned with holes 14. There is a continuing need for an accurate bonding and alignment process.